1. Field of the Invention
The present invention relates to a thin film element formed over a glass substrate and to a glass substrate over which a thin film element is formed.
2. Description of the Related Art
A glass substrate, which is low in cost as compared with a quartz substrate and easy to form in large size, has been frequently used as a substrate for a flat panel display and the like.
However, a glass substrate is low in heat distortion temperature and weak of heat, thus there are many restrictions in the process of forming a thin film semiconductor over a glass substrate. In view of this, in the case of forming polysilicon over a glass substrate, a process using laser crystallization is adopted so that the substrate is not heated much.
Nevertheless, the substrate is necessarily heated to a certain degree in order to, for example, activate impurities, thus various countermeasures to alleviate the heat shrink have been devised as disclosed in Patent Document 1 and Patent Document 2.
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-175984
[Patent Document 2]
Japanese Patent Laid-Open No. 2003-335547
In accordance with the cost reduction and enlargement of a display size, a glass substrate has gradually been enlarged, thereby causing considerable substrate distortion due to heat shrink. Thus, a further countermeasure is required.
In addition, as a design rule has been diminished, an acceptable margin for mask deviation has been smaller, thereby causing deviation in some cases due to misalignment or substrate distortion even if the mask is aligned with high precision.
In view of the foregoing, the invention provides a semiconductor element where the operation is not affected even when being formed over a substrate which is largely affected by heat shrink such as a large substrate. In addition, the invention provides a thin film semiconductor circuit and a thin film semiconductor device each provided with the semiconductor element.
In addition, according to the invention, a semiconductor element is provided where the operation is not affected even if there is slight mask deviation. Furthermore, the invention provides a thin film semiconductor circuit and a thin film semiconductor device each provided with the semiconductor element.